Messages in this thread |  | | | Date | Sun, 8 Nov 2009 13:51:35 +0100 | | From | Ingo Molnar <> | | Subject | Re: [PATCH 02/11] Add "handle page fault" PV helper. |
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* Avi Kivity <avi@redhat.com> wrote:
> On 11/08/2009 01:36 PM, Ingo Molnar wrote: > >>Three existing callbacks are: kmemcheck, mmiotrace, notifier. Two > >>of them kmemcheck, mmiotrace are enabled only for debugging, should > >>not be performance concern. And notifier call sites (two of them) > >>are deliberately, as explained by comment, not at the function entry, > >>so can't be unified with others. (And kmemcheck also has two different > >>call site BTW) > > > > We want mmiotrace to be generic distro capable so the overhead when > > the hook is not used is of concern. > > Maybe we should generalize paravirt-ops patching in case if (x) f() is > deemed too expensive.
Yes, that's a nice idea. We have quite a number of 'conditional callbacks' in various critical paths that could be made lighter via such a technique.
It would also free new callbacks from the 'it increases overhead even if unused' criticism and made it easier to add them.
Ingo
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